Unveiling the potential of bacterial isolates from plastic-polluted environments: enhancement of polyhydroxybutyrate biodegradation

This study explored the biodegradation potential of microbial isolates focusing on their ability to utilize biopolymers as sole carbon source. Previously described isolates have been investigated through agar-based screen for the ability to degrade plastic-related substrates in powder form, and four strains have been selected for further assessment. Polyhydroxybutyrate (PHB) films degradation was examined through liquid culture, soil burial and respirometry assays. Structural and chemical alterations in PHB were analysed using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The most successful strains were tested for the ability to degrade PHB/bacterial nanocellulose (BNC) blends. Bacillus sp. DG90 excelled in PHB degradation, achieving 60% weight loss in liquid culture, while Streptomyces sp. DG19 exhibited a notable degradation rate of 51 ± 1.7%. Soil burial assays underscored the impact of environmental factors on degradation rates, emphasizing the role of soil composition and nitrogen availability. In respirometry assay, PHB films were severely defragmented by Streptomyces sp. DG19 with overall weight loss of 83%, while for Bacillus sp. DG90, this percentage reached 39%. FTIR and DSC analyses suggested potential hydrolysis and structural alterations in treated samples. This study observed rapid PHB degradation (83% in 3 weeks) while, considering the complex composition of modern biomaterials, also showcased the potential of examined strains to degrade PHB-BNC blends up to 85%.